The present invention is directed to tool bit having a shank to be inserted into a chuck of a hand-held tool used in chiseling or chipping and/or drilling and/or percussion drilling. The shank has at least two rotary entrainment grooves not located diametrically opposite one another and the grooves extend to the end of the tool bit shank inserted into the chuck, so that rotary entrainment members in the chuck can engage in the rotary entrainment grooves. At least one locking groove, closed at its end closer to the end of the shank inserted into the chuck, is arranged to receive at least one locking member of the chuck for limiting axial movement of the tool bit.
Tool bits of this type are disclosed in DE-PS 2551125 and DE-PS 3717915. These tool bits are shaped so that they can be introduced into the chuck only in a very specific angular position. Tool bits according to DE-PS 3716915 have two diametrically opposed locking grooves closed at both ends. This arrangement is important, because tool bits in this patent publication must also fit into the tool bit chuck of the most widely sold heavy hammer-drill. In this hammer-drill, the transmission of torque as well as the locking action is provided by the two locking grooves disposed diametrically opposite one another.
In the short time since the introduction of hammer-drills and tool bits according to DE-PS 3716915 the disadvantage has been noted that wear, especially in the two rotary entrainment grooves, both lying between the two locking grooves, is very considerable. Considerable wear also takes place at the corresponding parts of the tool bit chuck. Due to such wear, the locking members and the locking grooves must transmit a considerable part of the torque. Again this leads, however, to premature damage to the tool bit chuck. Tool bit chuck damage not only results in considerable costs to the user, but also involves considerable work delays, since the repairs must be performed in a work shop. In addition, the largest possible working diameter of the drilling tool bit and the hand-held tool is limited in the upward direction, due to this wear susceptibility.